In the disclosure of the present invention reference is mostly made to the treatment of diabetes by delivery of insulin, however, this is only an exemplary use of the present invention.
Drug Injection devices have greatly improved the lives of patients who must self-administer drugs and biological agents. Drug Injection devices may take many forms, including simple disposable devices that are little more than an ampoule with an injection means or they may be highly sophisticated electronically controlled instruments with numerous functions. Regardless of their form, they have proven to be great aids in assisting patients to self-administer injectable drugs and biological agents. They also greatly assist care givers in administering injectable medicines to those incapable of performing self-injections.
In particular pen-style injection devices have proven to provide an accurate, convenient, and often discrete, way to administer drugs and biological agents, such as insulin. Modern devices have become more sophisticated and often include diverse and robust functions, such as memories for remembering time and amount of last dose, as well as, in the case of insulin devices, blood glucose monitors. While pen-style injection devices are typically cylindrically shaped with a needle protruding from the most distal portion of one end of the device, some devices have other shapes with the needle no longer protruding from the most distal part of an end of the device, e.g. Innovo® and InnoLet® from Novo Nordisk A/S, Bagsvaerd, Denmark.
Typically, injection devices use a pre-filled cartridge containing the medication of interest, e.g. 1.5 or 3.0 ml of insulin or growth hormone. The cartridge is typically in the form of a generally cylindrical transparent ampoule with a needle pierceable septum at one end and an opposed piston designed to be moved by the dosing mechanism of the injection device. The injection devices generally are of two types: “Durable” devices and “disposable” devices. A durable device is designed to allow a user to replace one cartridge with another cartridge, typically a new cartridge in place of an empty cartridge. In contrast, a disposable device is provided with an integrated cartridge which cannot be replaced by the user; when the cartridge is empty the entire device is discarded. Most injection devices are provided with a releasable pen cap covering and protecting the cartridge, the needle mount portion with the pierceable septum, and, as may be the case, a mounted needle assembly. To protect the needle the needle assembly it is normally provided with an inner needle cap.
Although it is recommended to use a needle assembly only once, it is well known that a number of users choose to leave the mounted needle assembly on after used and use it for a number of times. Also, some users actually using a given needle assembly only once prefer to pre-mount the needle assembly to have the delivery device ready for use when needed.
In both cases this means that the interior of the cartridge is in fluid communication with the exterior through the hollow needle penetrating the septum, this allowing air to enter the cartridge via the hollow needle during storage. As a consequence of this, it is recommended that users perform a so-called air shot removing potential air in the cartridge before an injection is performed.
Having regard to the above, it is an object of the present invention to provide a drug delivery device which in a simple and cost-effective manner either reduces the consequences of not performing an air shot or reduces the need to perform it when the device is stored between injections with a mounted needle assembly. The device should be simple, safe and convenient to use.